title: Liver × receptor ligands disrupt breast cancer cell proliferation through an E2F-mediated mechanism.
abstract: BACKGROUND
  Liver × receptors (LXRs) are members of the nuclear receptor family of ligand-dependent transcription factors and have established functions as regulators of cholesterol, glucose, and fatty acid metabolism and inflammatory responses. Published reports of anti-proliferative effects of synthetic LXR ligands on breast, prostate, ovarian, lung, skin, and colorectal cancer cells suggest that LXRs are potential targets in cancer prevention and treatment.
  
  
  METHODS
  To further determine the effects of LXR ligands and identify their potential mechanisms of action in breast cancer cells, we carried out microarray analysis of gene expression in four breast cancer cell lines following treatments with the synthetic LXR ligand GW3965. Differentially expressed genes were further subjected to gene ontology and pathway analyses, and their expression profiles and associations with disease parameters and outcomes were examined in clinical samples. Response of E2F target genes were validated by real-time PCR, and the posited role of E2F2 in breast cancer cell proliferation was tested by RNA interference experiments.
  
  
  RESULTS
  We observed cell line-specific transcriptional responses as well as a set of common responsive genes. In the common responsive gene set, upregulated genes tend to function in the known metabolic effects of LXR ligands and LXRs whereas the downregulated genes mostly include those which function in cell cycle regulation, DNA replication, and other cell proliferation-related processes. Transcription factor binding site analysis of the downregulated genes revealed an enrichment of E2F binding site sequence motifs. Correspondingly, E2F2 transcript levels are downregulated following LXR ligand treatment. Knockdown of E2F2 expression, similar to LXR ligand treatment, resulted in a significant disruption of estrogen receptor positive breast cancer cell proliferation. Ligand treatment also decreased E2F2 binding to cis-regulatory regions of target genes. Hierarchical clustering of breast cancer patients based on the expression profiles of the commonly downregulated LXR ligand-responsive genes showed a strong association of these genes with patient survival.
  
  
  CONCLUSIONS
  Taken together, these results indicate that LXR ligands target gene networks, including those regulated by E2F family members, are critical for tumor biology and disease progression and merit further consideration as potential agents in the prevention and treatment of breast cancers.
authors.forename: Trang
authors.initials: T
authors.lastname: Nguyen-Vu
authors.forename: Lise-Lotte
authors.initials: LL
authors.lastname: Vedin
authors.forename: Ka
authors.initials: K
authors.lastname: Liu
authors.forename: Philip
authors.initials: P
authors.lastname: Jonsson
authors.forename: Jean Z
authors.initials: JZ
authors.lastname: Lin
authors.forename: Nicholes R
authors.initials: NR
authors.lastname: Candelaria
authors.forename: Lindsay P
authors.initials: LP
authors.lastname: Candelaria
authors.forename: Sridevi
authors.initials: S
authors.lastname: Addanki
authors.forename: Cecilia
authors.initials: C
authors.lastname: Williams
authors.forename: Jan-Åke
authors.initials: JÅ
authors.lastname: Gustafsson
authors.forename: Knut R
authors.initials: KR
authors.lastname: Steffensen
authors.forename: Chin-Yo
authors.initials: CY
authors.lastname: Lin
mesh_terms: D001565:Benzoates / Q000008:administration & dosage / Q000378:metabolism*; D001596:Benzylamines / Q000008:administration & dosage / Q000378:metabolism*; D001943:Breast Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D050703:E2F2 Transcription Factor / Q000096:biosynthesis* / Q000378:metabolism; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008024:Ligands; D000071518:Liver X Receptors; D057093:Orphan Nuclear Receptors / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D014158:Transcription, Genetic / Q000187:drug effects
chemical_list: D001565:Benzoates; D001596:Benzylamines; D050703:E2F2 Transcription Factor; C493761:E2F2 protein, human; C473027:GW 3965; D008024:Ligands; D000071518:Liver X Receptors; D057093:Orphan Nuclear Receptors